The long range goal of this proposal is to determine the mechanisms of parathyroid hormone (PTH) and calcitonin (CT) secretion and action. Our specific objectives are to: 1) determine the total amino acid sequence of human PTH, develop improved methods for the isolation and radioiodination of PTH, develop a carboxyl-region specific radioimmunoassay of human PTH with general clinical utility and which can be distributed to endocrine laboratories worldwide, and determine the influence of serum concentrations of calcium on the glandular or peripheral metabolism of endogenous PTH; 2) determine the regulatory influences and interactions of calcium, adrenergic and cholinergic neurotransmitters on PTH secretion from normal and abnormal parathyroid tissue in vitro and 3) determine the physiologic means of modulation of PTH and CT receptor binding and nucleotide cyclase activation in bone and kidney cells in vivo and in vitro.